C5 Quick Revision Questions

C5 for AQA GCSE examination 2018 onwards

H = Higher tier only

SS = Separate science only

Question 1

• Define an exothermic reaction

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C5 for AQA GCSE examination 2018 onwards

• One that transfers energy to the surroundings so the temperature of the surroundings increases

Answer 1 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 2

• What is the energy needed to start a reaction?

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C5 for AQA GCSE examination 2018 onwards

• Activation energy

Answer 2 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 3

• Sketch a reaction profile for an endothermic reaction

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C5 for AQA GCSE examination 2018 onwards

Answer 3 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 4

• What three things can reaction profiles show?

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C5 for AQA GCSE examination 2018 onwards

• Relative energies of reactants and products

• Activation energy

• Overall energy change of a reaction

Answer 4 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 5

• Explain in an exothermic reaction in terms of bond breaking and making

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C5 for AQA GCSE examination 2018 onwards

• Less energy is needed to break bond than released on making new bonds

Answer 5 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 6

• What is the sum of the bond energies for 2 moles of the molecule below?

• C-H 412 kJ/mol

• C-C 368 kJ/mol

• C=O 532 kJ/mol

• C-O 352 kJ/mol

• H-O 465 kJ/mol

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C5 for AQA GCSE examination 2018 onwards

Answer 6 .... of 20

C5 for AQA GCSE examination 2018 onwards

• 2 (3 x C-H) = 2 (3 x 412) = 2472• 2 x C-C = 2 x 368 = 736• 2 x C=O = 2 x 532 = 1064• 2 x C-O = 2 x 352 = 704• 2 x H-O = 2 x 465 = 930

= 5906 kJ/mol

Question 7

• How does a cell between copper and zinc work?

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C5 for AQA GCSE examination 2018 onwards

• Copper is put into a solution of zinc ions

• Zinc metal will be deposited and copper metal will become copper ions in solution

• The difference is reactivity between the two metals will cause a change in voltage (seen through a voltmeter)

Answer 7 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 8

• What do batteries consist of?

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C5 for AQA GCSE examination 2018 onwards

• Two or more cells connected together in a series to provide a greater voltage

Answer 8 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 9

• Why can rechargeable cells and batteries be recharged?

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C5 for AQA GCSE examination 2018 onwards

• The chemical reactions are reversed when an external electrical current is supplied

Answer 9 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 10

• How is the voltage produced in terms of the relative reactivities of the two metals?

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C5 for AQA GCSE examination 2018 onwards

• The more reactive metal forces the less reactive metal to accept electrons. Voltages are based on the ‘relative’ reactivity of metals

Answer 10 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 11

A cell was set up with Ni electrodes in nickel(II) sulfate and silver electrodes in silver sulfate.

Write half equations for the reactions that occur at the electrodes

Ni forms Ni2+ ions and silver forms Ag+

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C5 for AQA GCSE examination 2018 onwards

• Ag2+ + e- Ag+

• Ni+ Ni2+ + e-

Answer 11 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 12

• What is special about fuel cells?

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C5 for AQA GCSE examination 2018 onwards

• They don’t need replacing or recharging like ordinary cells and batteries

Answer 12 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 13

• Write a balanced symbol equation for the reaction of hydrogen with oxygen

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C5 for AQA GCSE examination 2018 onwards

• 2H2 +O2 2H2O

Answer 13 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 14

• Why do hydrogen and oxygen not explode in a fuel cell?

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C5 for AQA GCSE examination 2018 onwards

• The energy released from the reaction is converted into electrical energy (very efficient process)

Answer 14 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 15

• Give two advantages of fuel cells

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C5 for AQA GCSE examination 2018 onwards

• Direct energy transfer (chemical energy into electrical energy). Energy does not have to be converted into heat first

• Fewer transfer stages

• Less polluting, as water is the product

• Fuel cells last longer than conventional rechargeable batteries

Answer 15 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 16

• What happens to the fuel in the fuel cell?

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C5 for AQA GCSE examination 2018 onwards

• The fuel is oxidised electrochemically within the fuel cell to produce a potential difference

Answer 16 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 17

• Why is the fuel cell reaction a redox reaction?

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C5 for AQA GCSE examination 2018 onwards

Electrons are gained and lost

Answer 17 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 18

• How would you go about measuring the amount of energy an alcohol gives as a fuel?

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C5 for AQA GCSE examination 2018 onwards

• Allow the energy to transfer into a body of water whilst burning the alcohol in oxygen

• Measure the temperature increase of the water

Answer 18 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 19

• What type of energy changes are:

• Bond breaking

• Bond making

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C5 for AQA GCSE examination 2018 onwards

• Bond breaking = endothermic

• Bond making = exothermic

Answer 19 .... of 20

C5 for AQA GCSE examination 2018 onwards

Question 20

• Tom investigates temperature changes during a reaction with cold acid. How could he

minimise heat losses?

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C5 for AQA GCSE examination 2018 onwards

• Put a lid on the beaker

• Insulate the beaker/vessel

Answer 20 .... of 20

C5 for AQA GCSE examination 2018 onwards